58 research outputs found
On the Coupling of the Meson to the Nucleon
The pseudoscalar and pseudovector coupling constants are calculated
from an effective vertex associated with the triangle diagram.
The predicted values are in agreement with the ones concluded from fitting
photoproduction amplitudes. In this context we stress the importance of
the properties of the scalar meson octet for meson physics.Comment: 11 pages LATEX and 2 postscript figures included in a self-extracting
uufile type archiv
Relativistic structure of one-meson and one-gluon exchange forces and the lower excitation spectrum of the Nucleon and the Delta
The lower excitation spectrum of the nucleon and is calculated in a
relativistic chiral quark model. Corrections to the baryon mass spectrum from
the second order self-energy and exchange diagrams induced by pion and gluon
fields are estimated in the field -theoretical framework. Convergent results
for the self-energy terms are obtained when including the intermediate quark
and antiquark states with a total momentum up to . Relativistic
one-meson and color-magnetic one-gluon exchange forces are shown to generate
spin 0, 1, 2, etc. operators, which couple the lower and the upper components
of the two interacting valence quarks and yield reasonable matrix elements for
the lower excitation spectrum of the Nucleon and Delta. The only contribution
to the ground state nucleon and comes from the spin 1 operators, which
correspond to the exchanged pion or gluon in the l=1 orbit, thus indicating,
that the both pion exchange and color-magnetic gluon exchange forces can
contribute to the spin of baryons. Is is shown also that the contribution of
the color-electric component of the gluon fields to the baryon spectrum is
enormously large (more than 500 MeV with a value ) and one needs
to restrict to very small values of the strong coupling constant or to exclude
completely the gluon-loop corrections to the baryon spectrum. With this
restriction, the calculated spectrum reproduces the main properties of the
data, however needs further contribution from the two-pion exchange and
instanton induced exchange (for the nucleon sector) forces in consistence with
the realistic NN-interaction models.Comment: 15 pages, 4 figures, 7 table
Relativistic Hamiltonians in many-body theories
We discuss the description of a many-body nuclear system using Hamiltonians
that contain the nucleon relativistic kinetic energy and potentials with
relativistic corrections. Through the Foldy-Wouthuysen transformation, the
field theoretical problem of interacting nucleons and mesons is mapped to an
equivalent one in terms of relativistic potentials, which are then expanded at
some order in 1/m_N. The formalism is applied to the Hartree problem in nuclear
matter, showing how the results of the relativistic mean field theory can be
recovered over a wide range of densities.Comment: 14 pages, uses REVTeX and epsfig, 3 postscript figures; a postscript
version of the paper is available by anonymous ftp at
ftp://carmen.to.infn.it/pub/depace/papers/951
N N bar,Delta bar N, Delta N bar excitation for the pion propagator in nuclear matter
The particle-hole and Delta -hole excitations are well-known elementary
excitation modes for the pion propagator in nuclear matter. But, the excitation
also involves antiparticles, namely, nucleon-antinucleon, anti-Delta-nucleon
and Delta-antinucleon excitations. These are important for high-energy momentum
as well, and have not been studied before, to our knowledge. In this paper, we
give both the formulas and the numerical calculations for the real and the
imaginary parts of these excitations.Comment: Latex, 3 eps file
NN interaction in a Goldstone boson exchange model
Adiabatic nucleon-nucleon potentials are calculated in a six-quark
nonrelativistic chiral constituent quark model where the Hamiltonian contains a
linear confinement and a pseudoscalar meson (Goldstone boson) exchange
interaction between quarks. Calculations are performed both in a cluster model
and a molecular orbital basis, through coupled channels. In both cases the
potentials present an important hard core at short distances, explained through
the dominance of the [51]_{FS} configuration, but do not exhibit an attractive
pocket. We add a scalar meson exchange interaction and show how it can account
for some middle-range attraction.Comment: 32 pages with 12 eps figures incorporated, RevTeX. Final version
published in PR
On the Relativistic Description of the Nucleus
We discuss a relativistic theory of the atomic nuclei in the framework of the
hamiltonian formalism and of the mesonic model of the nucleus. Attention is
paid to the translational invariance of the theory. Our approach is centered on
the concept of spectral amplitude, a function in the Dirac spinor space. We
derive a Lorentz covariant equation for the latter, which requires as an input
the baryon self-energy. For this we either postulate the most general
Lorentz-Poincar\'e invariant expression or perform a calculation via a
Bethe-Salpeter equation starting from a nucleon-nucleus interaction. We discuss
the features of the nuclear spectrum obtained in the first instance. Finally
the general constraints the self-energy should satisfy because of analyticity
and Poincar\'e covariance are discussed
Microscopic transition potential: Determination of and coupling constants
A transition potential, based on an effective
quark-quark interaction and a constituent quark cluster model for baryons, is
derived in the Born-Oppenheimer approach. The potential shows significant
differences with respect to those obtained by a direct scaling of the
nucleon-nucleon interaction. From its asymptotic behavior we extract the values
of and coupling constants in a
particular coupling schemeComment: 15 eps figures, Accepted for publication in Phys. Rev.
Consistent description of NN and pi-N interactions using the solitary boson exchange potential
A unified description of NN and pi-N elastic scattering is presented in the
framework of the one solitary boson exchange potential (OSBEP). This model
already successfully applied to analyze NN scattering is now extended to
describe pi-N scattering while also improving its accuracy in the NN domain. We
demonstrate the importance of regularization of pi-N scattering amplitudes
involving Delta isobars and derivative meson-nucleon couplings, as this model
always yields finite amplitudes without recourse to phenomenological form
factors. We find an empirical scaling relation of the meson self interaction
coupling constants consistent with that previously found in the study of NN
scattering. Finally, we demonstrate that the OSBEP model does not contradict
the soft-pion theorems of pi-N scattering.Comment: 29 pages RevTeX, submitted to Phys. Rev. C, further information at
http://i04ktha.desy.d
Correlation Between the Deuteron Characteristics and the Low-energy Triplet np Scattering Parameters
The correlation relationship between the deuteron asymptotic normalization
constant, , and the triplet np scattering length, , is
investigated. It is found that 99.7% of the asymptotic constant is
determined by the scattering length . It is shown that the linear
correlation relationship between the quantities and
provides a good test of correctness of various models of nucleon-nucleon
interaction. It is revealed that, for the normalization constant and
for the root-mean-square deuteron radius , the results obtained with the
experimental value recommended at present for the triplet scattering length
are exaggerated with respect to their experimental counterparts. By
using the latest experimental phase shifts of Arndt et al., we obtain, for the
low-energy scattering parameters (, , ) and for the
deuteron characteristics (, ), results that comply well with
experimental data.Comment: 19 pages, 1 figure, To be published in Physics of Atomic Nucle
Soft two-meson-exchange nucleon-nucleon potentials. I. Planar and crossed-box diagrams
Pion-meson-exchange nucleon-nucleon potentials are derived for two nucleons
in the intermediate states. The mesons we include are (i) pseudoscalar mesons:
; (ii) vector mesons: ; (iii) scalar
mesons: ; and (iv) the
contribution from the Pomeron. Strong dynamical pair suppression is assumed,
and at the nucleon-nucleon-meson vertices Gaussian form factors are
incorporated into the relativistic two-body framework using a dispersion
representation for the pion- and meson-exchange amplitudes. The Fourier
transformations are performed using factorization techniques for the energy
denominators. The potentials are first calculated in the adiabatic
approximation to all planar and crossed three-dimensional momentum-space
-meson diagrams. Next, we calculate the corrections.Comment: 28 pages RevTeX, 8 postscript figures; revised version as to appear
in Phys. Rev.
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